Plywood vs. OSB I-Joists

Q.Do any I-joist
manufacturers still use plywood webs? At my local
lumberyard, I was told that manufacturers switched from
plywood to OSB webs because the plywood tended to
delaminate, but I suspect the real reason is that OSB
is cheaper. I'd prefer to use plywood I-joists, because
I think they'd be stronger.

A.Paul Fisette, director
of Building Materials and Wood Technology at the
University of Massachusetts Amherst and a JLC
contributing editor, responds: While you might
be able to find a small manufacturer somewhere who
still makes I-joists with plywood webs, the major
players do not. It may be true that OSB-web
I-joists cost somewhat less to manufacture, but the
main reason for the change is that OSB webs provide
superior structural performance. OSB has
interlocking fibers that transfer shear loads
better than plywood does, making it much stronger
in shear. As a result of this difference, you can
cut larger holes in the OSB webs than in plywood
webs, and OSB is capable of transferring greater
loads to bearing points.

The OSB in I-joist webs is not the
garden-variety OSB used for sheathing products. It
has more wax and about 15 percent more resin,
making it a very stable material. In fact, instead
of being a cheaper substitute for plywood, I-joists
made with OSB webs mark a significant improvement
in the structural floor-framing industry.